WASHINGTON (Reuters) - President Barack Obama said on Tuesday the U.S. government had sent "very direct messages" to Iran warning it not to send weapons to Yemen that could be used to threaten shipping traffic in the region.

The Pentagon said on Tuesday the presence of a large convoy of Iranian cargo ships in the Arabian Sea was one factor in the U.S. decision to deploy additional warships in the waters off war-torn Yemen.

But Army Colonel Steve Warren, a Pentagon spokesman, dismissed reports the carrier USS Theodore Roosevelt and cruiser USS Normandy had been sent to the region to intercept Iranian ships carrying arms to Iranian-backed Houthi rebels fighting forces loyal to the U.S.-backed Yemeni president.

In a televised interview on Tuesday on MSNBC's "Hardball," Obama said Washington had been "very straightforward" with Tehran about the issue.

"Right now their ships are in international waters. There's a reason why we keep some of our ships in the Persian Gulf region and that is to make sure that we maintain freedom of navigation," Obama said.

""What we've said to them is that, 'If there are weapons delivered to factions within Yemen that could threaten navigation, that's a problem,'" he added. "And we're not sending them obscure messages. We send them very direct messages about it."

The Pentagon spokesman Warren said he did not believe Navy warships patrolling the region had been in direct contact with the Iranian flotilla of nine cargo ships.

He said the United States did not know what the Iranian cargo ships were carrying and declined to say whether the U.S. warships would stop and board Iranian vessels if they attempted to enter Yemeni territorial waters.

"I'm not going to telegraph anything," Warren said.

The Shiite Muslim Houthis sidelined the central government after seizing the capital, Sana'a, in September and occupying a broad swath of Yemen, which borders oil giant Saudi Arabia.

The U.N. Security Council imposed an arms embargo on the Houthi rebels, and the Saudi navy has imposed a naval blockade around Yemen.

Saudi Arabia said on Tuesday it was ending a month-long campaign of air strikes against the Houthi rebels and would back a political solution to the conflict, an announcement the White House welcomed.